Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $87.75   6.275%   $93.2563   $93.26   $93.25   $93.30  
  Purchase #2 $145.81   4.179%   $151.9034   $151.90   $151.90   $151.90  
  Purchase #3 $74.28   4.455%   $77.5892   $77.59   $77.60   $77.60  
  Purchase #4 $131.98   3.790%   $136.982   $136.98   $137.00   $137.00  
  Purchase #5 $192.59   8.699%   $209.3434   $209.34   $209.35   $209.30  
  Purchase #6 $59.41   3.124%   $61.266   $61.27   $61.25   $61.30  
  Purchase #7 $18.87   3.386%   $19.5089   $19.51   $19.50   $19.50  
  7 purchase totals = $710.69       $749.8492   $749.85   $749.85   $749.90